1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * isochronous resources helper functions
4 *
5 * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
6 */
7
8 #include <linux/device.h>
9 #include <linux/firewire.h>
10 #include <linux/firewire-constants.h>
11 #include <linux/export.h>
12 #include <linux/jiffies.h>
13 #include <linux/mutex.h>
14 #include <linux/sched.h>
15 #include <linux/spinlock.h>
16 #include "iso-resources.h"
17
18 /**
19 * fw_iso_resources_init - initializes a &struct fw_iso_resources
20 * @r: the resource manager to initialize
21 * @unit: the device unit for which the resources will be needed
22 *
23 * If the device does not support all channel numbers, change @r->channels_mask
24 * after calling this function.
25 */
26 int fw_iso_resources_init(struct fw_iso_resources *r, struct fw_unit *unit)
27 {
28 r->channels_mask = ~0uLL;
29 r->unit = unit;
30 mutex_init(&r->mutex);
31 r->allocated = false;
32
33 return 0;
34 }
35 EXPORT_SYMBOL(fw_iso_resources_init);
36
37 /**
38 * fw_iso_resources_destroy - destroy a resource manager
39 * @r: the resource manager that is no longer needed
40 */
41 void fw_iso_resources_destroy(struct fw_iso_resources *r)
42 {
43 WARN_ON(r->allocated);
44 mutex_destroy(&r->mutex);
45 }
46 EXPORT_SYMBOL(fw_iso_resources_destroy);
47
48 static unsigned int packet_bandwidth(unsigned int max_payload_bytes, int speed)
49 {
50 unsigned int bytes, s400_bytes;
51
52 /* iso packets have three header quadlets and quadlet-aligned payload */
53 bytes = 3 * 4 + ALIGN(max_payload_bytes, 4);
54
55 /* convert to bandwidth units (quadlets at S1600 = bytes at S400) */
56 if (speed <= SCODE_400)
57 s400_bytes = bytes * (1 << (SCODE_400 - speed));
58 else
59 s400_bytes = DIV_ROUND_UP(bytes, 1 << (speed - SCODE_400));
60
61 return s400_bytes;
62 }
63
64 static int current_bandwidth_overhead(struct fw_card *card)
65 {
66 /*
67 * Under the usual pessimistic assumption (cable length 4.5 m), the
68 * isochronous overhead for N cables is 1.797 µs + N * 0.494 µs, or
69 * 88.3 + N * 24.3 in bandwidth units.
70 *
71 * The calculation below tries to deduce N from the current gap count.
72 * If the gap count has been optimized by measuring the actual packet
73 * transmission time, this derived overhead should be near the actual
74 * overhead as well.
75 */
76 return card->gap_count < 63 ? card->gap_count * 97 / 10 + 89 : 512;
77 }
78
79 static int wait_isoch_resource_delay_after_bus_reset(struct fw_card *card)
80 {
81 for (;;) {
82 s64 delay = (card->reset_jiffies + HZ) - get_jiffies_64();
83 if (delay <= 0)
84 return 0;
85 if (schedule_timeout_interruptible(delay) > 0)
86 return -ERESTARTSYS;
87 }
88 }
89
90 /**
91 * fw_iso_resources_allocate - allocate isochronous channel and bandwidth
92 * @r: the resource manager
93 * @max_payload_bytes: the amount of data (including CIP headers) per packet
94 * @speed: the speed (e.g., SCODE_400) at which the packets will be sent
95 *
96 * This function allocates one isochronous channel and enough bandwidth for the
97 * specified packet size.
98 *
99 * Returns the channel number that the caller must use for streaming, or
100 * a negative error code. Due to potentionally long delays, this function is
101 * interruptible and can return -ERESTARTSYS. On success, the caller is
102 * responsible for calling fw_iso_resources_update() on bus resets, and
103 * fw_iso_resources_free() when the resources are not longer needed.
104 */
105 int fw_iso_resources_allocate(struct fw_iso_resources *r,
106 unsigned int max_payload_bytes, int speed)
107 {
108 struct fw_card *card = fw_parent_device(r->unit)->card;
109 int bandwidth, channel, err;
110
111 if (WARN_ON(r->allocated))
112 return -EBADFD;
113
114 r->bandwidth = packet_bandwidth(max_payload_bytes, speed);
115
116 retry_after_bus_reset:
117 spin_lock_irq(&card->lock);
118 r->generation = card->generation;
119 r->bandwidth_overhead = current_bandwidth_overhead(card);
120 spin_unlock_irq(&card->lock);
121
122 err = wait_isoch_resource_delay_after_bus_reset(card);
123 if (err < 0)
124 return err;
125
126 mutex_lock(&r->mutex);
127
128 bandwidth = r->bandwidth + r->bandwidth_overhead;
129 fw_iso_resource_manage(card, r->generation, r->channels_mask,
130 &channel, &bandwidth, true);
131 if (channel == -EAGAIN) {
132 mutex_unlock(&r->mutex);
133 goto retry_after_bus_reset;
134 }
135 if (channel >= 0) {
136 r->channel = channel;
137 r->allocated = true;
138 } else {
139 if (channel == -EBUSY)
140 dev_err(&r->unit->device,
141 "isochronous resources exhausted\n");
142 else
143 dev_err(&r->unit->device,
144 "isochronous resource allocation failed\n");
145 }
146
147 mutex_unlock(&r->mutex);
148
149 return channel;
150 }
151 EXPORT_SYMBOL(fw_iso_resources_allocate);
152
153 /**
154 * fw_iso_resources_update - update resource allocations after a bus reset
155 * @r: the resource manager
156 *
157 * This function must be called from the driver's .update handler to reallocate
158 * any resources that were allocated before the bus reset. It is safe to call
159 * this function if no resources are currently allocated.
160 *
161 * Returns a negative error code on failure. If this happens, the caller must
162 * stop streaming.
163 */
164 int fw_iso_resources_update(struct fw_iso_resources *r)
165 {
166 struct fw_card *card = fw_parent_device(r->unit)->card;
167 int bandwidth, channel;
168
169 mutex_lock(&r->mutex);
170
171 if (!r->allocated) {
172 mutex_unlock(&r->mutex);
173 return 0;
174 }
175
176 spin_lock_irq(&card->lock);
177 r->generation = card->generation;
178 r->bandwidth_overhead = current_bandwidth_overhead(card);
179 spin_unlock_irq(&card->lock);
180
181 bandwidth = r->bandwidth + r->bandwidth_overhead;
182
183 fw_iso_resource_manage(card, r->generation, 1uLL << r->channel,
184 &channel, &bandwidth, true);
185 /*
186 * When another bus reset happens, pretend that the allocation
187 * succeeded; we will try again for the new generation later.
188 */
189 if (channel < 0 && channel != -EAGAIN) {
190 r->allocated = false;
191 if (channel == -EBUSY)
192 dev_err(&r->unit->device,
193 "isochronous resources exhausted\n");
194 else
195 dev_err(&r->unit->device,
196 "isochronous resource allocation failed\n");
197 }
198
199 mutex_unlock(&r->mutex);
200
201 return channel;
202 }
203 EXPORT_SYMBOL(fw_iso_resources_update);
204
205 /**
206 * fw_iso_resources_free - frees allocated resources
207 * @r: the resource manager
208 *
209 * This function deallocates the channel and bandwidth, if allocated.
210 */
211 void fw_iso_resources_free(struct fw_iso_resources *r)
212 {
213 struct fw_card *card;
214 int bandwidth, channel;
215
216 /* Not initialized. */
217 if (r->unit == NULL)
218 return;
219 card = fw_parent_device(r->unit)->card;
220
221 mutex_lock(&r->mutex);
222
223 if (r->allocated) {
224 bandwidth = r->bandwidth + r->bandwidth_overhead;
225 fw_iso_resource_manage(card, r->generation, 1uLL << r->channel,
226 &channel, &bandwidth, false);
227 if (channel < 0)
228 dev_err(&r->unit->device,
229 "isochronous resource deallocation failed\n");
230
231 r->allocated = false;
232 }
233
234 mutex_unlock(&r->mutex);
235 }
236 EXPORT_SYMBOL(fw_iso_resources_free);
237
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